Holesaws are used with power drills to make large diameter holes in relatively thin materials with limited machine power, since they convert only a limited annular region to sawdust and chips. Traditionally, holesaws comprise an arbor with one or more threaded areas, a central pilot drill attached to the arbor, an axially movable pin support which is rotationally locked to the arbor and provided with one or more pins, and a bell-shaped holesaw blade which is made to rotate with the arbor by the pins penetrating pin holes in a flat top of the bell. The rotational locking of the pin support to the arbor occurs usually by having a profiled hole in the pin support slide along a correspondingly profiled part of the arbor as in patents U.S. Pat. Nos. 4,063,560 and 5,076,741, or by having a flange fixed to the arbor acting directly on the pins as in patents U.S. Pat. Nos. 4,669,928 and 4,968,189. The upper shank of the arbor is made for easy attachment to the power drill, conical, cylindrical or hexagonal.
One common demand when using holesaws is that it should be possible to exchange the sawblade without removing the other components from the power drill. For this purpose the sawblade has a threaded center hole attached to a threaded end of the arbor, and can be quickly removed by rotating it after moving the pin support axially to disengage the pins from the top of the bell. To allow drilling vertically upwards, the pin support must be securable against unintentional displacement, as by a locking spring in U.S. Pat. No. 4,036,560 or by a nut as in U.S. Pat. No. 4,669,928.
The holesaw is rotationally guided by the pins and axially by the threaded center hole. Modem sawblades are often made from thin walled material, which makes the thread prone to wear, and the top of the bell has a low stiffness for axial and tilting motions. Therefore, it is preferred to press an end surface of the pin support against the top of the bell by a snap lock spring as in U.S. Pat. No. 4,036,560, by a spring loaded washer as in U.S. Pat. No. 3,784,316 or by a nut as in U.S. Pat. No. 3,758,221. It has also been suggested in application SE 95 03797-4 to press against the top of the bell the end of a tubular sleeve located concentrically outside the pin support by rotation of the same nut that secures the pin support axially, in order to apply the force at a greater radius measured from the arbor.
All mown designs of holesaws have disadvantages in common. If they use a nut or a spring loaded washer, two hands are needed for changing sawblade. If they use a snap lock spring, neither the size nor the symmetry of the load is controlled. The present invention concerns a new type of holesaw where a change of sawblade can be made with one hand.